1. Field of the Invention
The present invention relates to a method for comparing images, and particularly to a system and method for comparing dental X-ray images.
2. Description of the Related Art
Dental radiographs are used for the purpose of finding a slight change in the internal structure of a bone, monitoring the progress of a disease, developing treatment policies, or determining an identity (see Lehmann, T. M., Grondahl, H. G., & Benn, D. K. (2000). Computer-based registration for digital subtraction in dental radiology. Dentomaxillofacial Radiology, 29, 323-346., for example). When dental radiographs are used for any one of these purposes, a radiograph taken several weeks ago or several years ago needs to be accurately compared with a radiograph taken recently. In order to realize a computer-aided diagnosis (CAD) in a dental treatment, it is important that a dental radiograph taken recently should be accurately positioned to a dental radiograph taken in the past. However, because dental radiographs are taken with the films placed in the complicated and narrow oral cavity, a nonlinear distortion exists between the dental radiograph taken recently and the dental radiograph taken in the past, even though the dental radiographs are taken of the same oral cavity of the same person. This brings about a problem that it is difficult to compare the dental radiograph taken recently and the dental radiograph taken in the past.